An unannotated Java method returns a platform String type. Which first step keeps the Kot…

An unannotated Java method returns a platform String type. Which first step keeps the Kotlin boundary honest when the implementation is not trusted?

1. Assign it to String? and validate or normalize it.
2. Assign it to String and rely on compiler inference.
3. Append !! so later calls can omit safe calls.
4. Cast it with as String because platform types are always non-null.